Recently, mobile communications terminals, electronic appliances, etc. having various functions and high performance have been getting required to be smaller and lighter, so that electronic parts are disposed in a narrower space at higher density, with their speeds increasing. Accordingly, among circuits and parts, electromagnetic wave noises, particularly high-frequency noises of several hundreds of MHz to several GHz have become serious problems. To suppress such near-field electromagnetic wave noises, various electromagnetic-wave-absorbing films have been proposed and put into practical use.
Such electromagnetic-wave-absorbing films mostly contain magnetic materials and/or conductive materials. For example, JP 2010-153542 A discloses an electromagnetic-wave-absorbing film comprising a substrate; a conductive layer formed by a conductive coating material containing particles, flakes or thin wires of metals such as Cu, etc. or carbon; and a magnetic layer formed by a magnetic coating material containing soft-magnetic materials such as ferrite, Sendust, permalloy, etc. However, the electromagnetic-wave-absorbing film disclosed in JP 2010-153542 A is expensive because of having the conductive layer and the magnetic layer, and does not have sufficient absorbability to electromagnetic wave noises of several hundreds of MHz to several GHz.
JP 2006-114877 A discloses an electromagnetic-wave-absorbing sheet obtained by applying an electromagnetic-wave-absorbing coating composition to at least one surface of a substrate sheet made of silicone resins, acrylic resins, polyimide resins, phenol resins, urethane resins, PET, etc.; the electromagnetic-wave-absorbing coating composition comprising (a) 100 parts by weight of a carbon nano-material such as carbon nanotube, carbon nanohom, graphite nanofibers, carbon nanofibers, etc., (b) 50-1000 parts by weight of a resin component such as thermoplastic resins such as ABS resins, polyvinylidene fluoride, polyamides, polyimides, polyethylene terephthalate, polycarbonates, polyvinyl chloride, etc., thermosetting resins such as epoxy resins, phenol resins, etc., or UV-curing resins such as polyesters, polyvinyl butyral, acrylics, phenols, polyurethanes, etc., and (c) 50-3000 parts by weight of an organic solvent such as ketones, saturated hydrocarbons, aromatic hydrocarbons, glycol ethers, glycol etheresters, alcohols, etc. However, the electromagnetic-wave-absorbing sheet disclosed in JP 2006-114877 A does not have sufficient absorbability to electromagnetic wave noises of several hundreds of MHz to several GHz.